Method and apparatus for forming normally appearing stitches

ABSTRACT

In a sewing machine having thread stitch forming instrumentalities for forming successive stitches in a workpiece and having means for moving the workpiece in vector directions and wherein the stitch forming instrumentalities may produce stitch abnormalities in at least one of the vector directions of workpiece movement, a method of forming normally appearing stitches by tensioning the stitch forming thread in response to the vector direction of workpiece movement. The method may also include drawing the stitch abnormalities into the workpiece. Apparatus for carrying out the foregoing method has means responsive to the vector direction of workpiece movement for controlling variable thread tensioning means included in the stitch forming instrumentalities.

United States Patent 1 91 1111 3,827,382

De Vita et al. 1 Aug. 6, 1974 [54] METHOD AND APPARATUS FOR FORMING917,886 9/1954 Germany 1 12/255 NORMALLY APPEARING STITCHES [75]Inventors: Raymond A. DeVita, Hamilton; Primary Examiner-Werner H.Schroeder Adolph S. Dorosz, Beverly; Henry Attorney, Agent, orFirm-Ralph D. Gelling; Vincent M. Scaletti, .ir., Wenham, all of A.White; Richard B. Megley Mass. 1

[73] Assignee: USM Corporation, Boston, Mass.

[22] Filed: Oct. 24, 1972 [2]] Appl. No.: 299,945

[ 5 7 ABSTRACT In a sewing machine having thread stitch forminginstrumentalities for forming successive stitches in a workpiece andhaving means for moving the work- [52] US. Cl Ill/2 1 12 1 55 piece invector directions and wherein the stitch forml l D053) D051) /0 inginstrumentalities may produce stitch abnormalities [58] Field of Search112/2, 77, 79, 102, 103, in at least one of the vector directions ofworkpiece 112/117, 118, 119, 121.12, 181, 185, 203, movement, a methodof forming normally appearing 262 stitches by tensioning the stitchforming thread in response to the vector direction of workpiece move-[56] References Cited ment. The method may also include drawing thestitch UNITED STATES P T abnormalities into the workpiece. Apparatus forcarry- 1 ()81 596 12/1913 Finch 112 255 x ing out the foregoing methodhas mews responsive to 3,082,722 3/1963 Tateishi 112/181 the Vectordirection of workpiece movement for 3,528,379 9/1970 Miller 112/254 Xtrolling variable thread tensioning means included in 3,724,409 4/1973Olney, Jr. 112/255 the stitch forming instrumentalities.

FORElGN PATENTS OR APPLICATIONS 1,902,711 8/1970 Germany 112/255 6Claims, 4 Drawing Figures FAIENTEBMIG 3.827. 382

SHEEI 1 0F 2 Pmmzmm: mm 3.827, 382

SHEEI 2 [IF 2 J8 L53 1 l Xi Yi I Point Daia Call 517M 54 HITEN fsiiil HTI J6 Tension Data BACKGROUND OF THE INVENTION This invention relates toa method and apparatus for forming normally appearing stitches withthread.

Efforts to automate sewing machines and other stitch forming deviceshave recently increased as the cost and difficulty of obtaining skilledsewing machine operators has increased. Many of these efforts atautomating sewing operations such as those described in copending U. S.Pat. No. 3,742,879 granted July 3, 1973, in the names of Hans F.Schaefer, Jr. and Reade Williams, have included means for automaticallymoving a workpiece relative to stitch forming instrumentalities of thesewing machine.

The means for moving a workpiece described in the above applicationdiffer from those traditionally employed in sewing machines in that theunidirectional, reciprocating workpiece moving means or feed dogstraditionally employed are replaced by means for moving the workpiece inmultiple vector directions, usually along substantially orthogonalcoordinates designated X and Y. The new workpiece moving means may beappropriately and automatically controlled to cause relative motionbetween the workpiece and stitch forming instrumentalities along apredetermined path which may include all vector directions relative tothe stitch forming instrumentalities within the plane defined by theorthogonal coordinates. In contrast, the feed dogs and manual controltraditionally employed in sewing machines produce relative movementbetween a workpiece and the stitch forming instrumentalities havingvector directions essentially tangential to the path being sewn.

As further described in copending U. S. application Ser. No. 192,288filed Oct. 26, 1971 in the name of Hans F. Schaefer, Jr., movement ofthe workpiece relative to stitch forming instrumentalities along a widerange of vector directions may produce stitch abnormalities evidenced byan extra twist or half-hitch in the completed stitch. Accordingly, thisproblem is called half-hitching. The half-hitch gives a canted, abnormalappearance to the completed stitch.

A further problem resulting from the wide range of vector directions ofworkpiece movement is variably increased binding or snagging of thestitch forming thread in certain vector directions of workpiecemovement. As the workpiece is moved relative to the stitch forminginstrumentalities, the stitch last formed in the workpiece draws threadfrom storage spools associated with the instrumentalities in a directionhaving a vector component in the direction in which the workpiece hascarried the last formed stitch. In certain of these directions, thethread is drawn into frictional engagement with a side of a needleincluded in the stitch forming instrumentalities. Frictional engagementof the needle and thread binds the thread against movement from thestorage spools and may prevent other stitch forming instrumentalitiesfrom forming a normally appearing stitch. Similarly, a half-hitch formedin the stitch will bind in a hole in the workpiece formed by the needleto strongly resist being drawn into the workpiece. On the other hand,where such binding does not occur, increased thread tension intended toovercome binding where it occurs may destroy a stitch originallynormally formed by drawing it completely through the workpiece, givingan abnormal appearance. Accordingly, these problems are called threadbinding. Both halfhitching and binding are stitch abnormalities.

SUMMARY OF THE INVENTION tus for carrying out the foregoing method hasmeans responsive to the vector direction of workpiece movement between aselected pair of stitches for controlling variable thread tensioningmeans included in traditional stitch forming instrumentalities.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of theinvention which is intended to illustrate and not to limit the inventionwill now be described in relation to drawings of the embodiment, inwhich:

FIG. 1 is a perspective view of an automatically controlled sewingmachine having means for practicing the invention;

FIG. 2 is a perspective view of the machine in FIG. 1 showing inenlarged scale elements embodying a portion of the invention;

FIG. 3 is a graphical illustration of a control function of theinvention; and

FIG. 4 is a flow diagram of a control function of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodimentillustrated in FIG. 1 has a sewing machine generally at 10 similar,except as hereinafter described, to well known, commercially availableelectrically powered lockstitch or chain stitch sewing machines. Thesewing machine includes stitch forming instrumentalities generally at 12of the type well known in the art including a needle 14 for periodicallypenetrating a workpiece l6 and carrying thread (not shown) through theworkpiece to form a series of stitches 18 in the workpiece.

Apparatus generally at 20 for moving the workpiece relative to thesewing instrumentalities differs from that traditionally employed withsewing machines in that the traditional feed dogs are replaced by aworkpiece support 22 mounted generally normally to a longitudinal axisof the needle for movement relative to the sewing instrumentalities on arack 24 engaged by an electrically driven pinion 26 operatively mountedon another, generally orthogonal pinion driven rack (not shown).

A control generally at 28 is appropriately connected to the electricaldrive means for the pinions of the workpiece moving apparatus to controldriving movement of the pinions. Appropriate control of the piniondriving means may then produce movement of the workpiece 16 relative tothe needle 14 along vector directions extending 360 about the plane ofthe workpiece on the support 22. Movement about the plane of theworkpiece support 22 iis conveniently dimensioned according toorthogonal X and Y coordinate axes superimposed on the support andcorresponding to directions of movement implemented by each of thegenerally orthogonal racks of the workpiece moving means. As with aconventional sewing machine, each workpiece movement is followed bystitch forming penetration of the workpiece by the needle to form asuccession of thread stitches divided by needle penetration points onthe workpiece.

The sewing machine generally at also differs from traditional sewingmachines in the provision of means generally at 30 for variablytensioning thread passing through the needle. As better seen in FIG. 2,the variable thread tensioning means comprise a thread tensioning device32 linearly actuatable by a plunger 34 to provide either of twopreselected tensions to a thread (not shown) wrapped about thetensioning device. Such tensioning devices and other variable threadtensioning devices are well known in the art and commercially available.A bell crank 36 is pivotally secured to a frame of the sewing machineand positioned to drive the plunger 34 against the action of a returnspring in the device 32 into one of two thread tension selectingpositions of the plunger 34. A rod 38 of a linear actuator 40 engagesanother arm of bell crank 36 to pivot the bell crank for driving theplunger 34. The linear actuator 40 may be an electrical solenoid for apneumatic piston and cylinder, many types of which are well known in theart and commercially available. The actuator 40 is appropriatelyconnected to the control 28 to operatively drive the tension settingplunger 34 in response to a signal from the control 28.

The two tensions provided the needle thread by tensioning device 32 arepreselected to appropriately cooperate with other well known threadtensioning means of the stitch forming instrumentalities generally at12, such as lever and cam or rotary thread take-up devices. Thesetensioning means of the stitch forming instrumentalities draw alast-formed stitch tightly against a workpiece to form a secure stitchby tensioning the thread forming a stitch in the workpiece l6 andrunning through the needle 14 to the thread tensioner 32 and back to itsstorage spool (not shown). If the thread tension device 32 provides alow tension, the thread takeup will draw more thread from the spool andapply a lower tension to the thread at the workpiece 16. On the otherhand, if the thread tension device 32 provides a high tension, lessthread can be drawn from the spool and a higher tension will be appliedto the thread at the workpiece.

Then, according to the method of the invention, a high tension isapplied when the stitch forming instrumentalities form a stitchabnormality such as a halfhitch to draw the half-hitch into theworkpiece. The tension is preselected to draw the half-hitch interior ofthe workpiece, lodging it in the needle hole, so as to make thehalf-hitch invisible and to give the visible portion of the stitch anormal appearance. Similarly, a high tension on the thread from threadtension device 32 permits the thread to be drawn against binding of thethread on the needle to produce a tight, normally appearing stitch. Onthe other hand, where there is no half-hitching or binding, a lowertension is provided by the thread tensioning device 32 to permit normalformation of a stitch with normal appearance without drawing the stitchcompletely through the workpiece as would result with the highertension. Accordingly, normally appearing stitches are formed whether thestitch forming instrumentalities form half-hitches, bind against thethread, or do neither.

The control 28 controls the variable thread tensioning device 32 toprovide an appropriate tension for each stitch formed by thestitch-forming instrumentalities of the sewing machine. In the preferredembodiment the control 28 is an appropriately programed, commerciallyavailable, general purpose digital computer operatively associated witha commercially available numerical control. In the preferred embodimentthe control 28 also functions to direct movement of the workpiece andtherefore generates a pair of X Y coordinate values for each needlepenetration point on the workpiece demarking the beginning and endpoints for each stitch. For example, points 42 and 44 shown in FIG. 3have coordinate values (X1, Y1) and (X2, Y2), respectively, relative tocoordinate axes X and Y superimposed on the workpiece. However, in analternative embodiment, shaft encoders operatively connected to theracks of the workpiece moving apparatus may provide point coordinatevalues as known in the art. The vector direction of workpiece movementfor forming a stitch between the needle engaging points will be on avector direction line 46 connecting the points. This vector will form anangle AG with a selected reference coordinate axis, here the Y axis.Similarly, angles 48 and 50 are predetermined to define zones of vectordirections of workpiece movement which will not or will, respectively,cause the stitch forming instrumentalities to produce half-hitching and-/or binding. Accordingly, a predetermined higher or lower thread tensionfrom the variable thread tensioning device 32 may be associated witheach zone. Angles HT defining extremities of these zones are stored inthe control 28 for reference.

Referring now to FIG. 4, a program for the control 28 generally at 52includes a sub-routine 54 called HITEN which appears in the controlprogram for the formation of each stitch. The main program portion 54first calls the particular HITEN sub-routine 56. The HITEN sub-routinethen calls the X Y coordinate axis values for the points beginning andending the stitch, calculates the angle AG, and then calls for theangles HT defining the zones of vector directions associated with eachtension to be applied by the tensioning device 32. The sub-routinecompares the angle AG of the particular stitch with those defining thetension zones and determines which zone associated tension correspondsto the particular angle AG. It then provides an appropriate signalcommunicated to the linear actuator 40 to drive the tension device 32into the tension position associated with the signal.

In accordance with the flow diagram, a particular program for thesub-routine HITEN provides a signal T equal to a logic zero for thelower tension position of the tension device 32 and a signal T equal toa logic one for the higher tension. Input parameters provided thesub-routine are a pair of X Y coordinate values for of the pointsbeginning and ending a particular stitch and stored array of angle HTpairs defining zones of angles associated with each of the tension Tsignals. The particular sub-routine in block 56 of FIG. 4 then may be:

Sub-routine HITEN (X1, Y1, X2, Y2, HT, T) Dimension HT (4, 2)

DY Y2 Y1 AG ATAN (ABS (DY)/ABS (DX)) 1F (DX) 10, 20, 20 1F (DY) 11,12,12 11 AG 180.+AG

Go to 22 12 AG 180.AG

Go to 22 IF (DY) 21, 23, 22 21 AG 360.-AG

Go to 22 23 IF (DX) 25, 25, 22

25 Write (1,100) 100 Format Error DX, DY 0) Go to 50 22 DO 1 1, Y

[F (AG l-lT (l, 1)) 30, 32, 31 31 IF (AG HT (1, 2)) 32, 32, 30 30Continue Go to 50 32 T 1 50 Return End.

In alternative embodiments of the invention, the control 28 may be otherthan the above described general purpose digital computer and associatednumerical control. For example, the control may be a special purposedigital computer or an analog computer appropriately programed as knownby those skilled in the art to provide appropriate signals for theactuator 40. Similarly, the numerical control operatively associatedwith a computer, for example by reading a signal T for generating asignal for the actuator from an instruction medium such as punched ormagnetic tape prepared by the computer, may be replaced by the generalpurpose digital computer itself. Preparation of such a numerical controltape may also be done manually in accordance with the teachings of theinvention or by a separately located, tape preparing computer of one ofthe other above types. Still further, it will be appreciated that thecontrol 28 could be a mechanical arrangement using cams or other devicesto generate a signal appropriate for the linear actuator to drive thetensioning device 32. The latter mechanical arrangement may beparticularly useful with sewing machines having mechanical workpieceguiding controls such as known bar tackers.

It will be appreciated that the particular thread tension for forming aparticular stitch may be set prior to formation of the particularstitch, concurrently with the formation of the particular stitch orimmediately after the formation of the particular stitch in accordancewith the operation of the particular thread tension means in the stitchforming instrumentalities of a particular sewing machine. The timing ofsuch tension setting in the program of the preferred embodiment may beselected by determining the position of the HITEN sub-routine in themain control program. It may be similarly set by appropriateorganization of the other devices described as alternative embodimentsof the control. Such sequence setting is well within the skill of theart.

Still further alternative embodiments, including, for example, more thantwo tension zones or more than two predetermined tension variations inthe tensioning device, are contemplated to be within the scope of theinvention defined by the following claims:

We claim:

1. A method of forming a normally appearing stitch with a thread in arelatively movable workpiece and thread, comprising the steps of:forming a stitch in the workpiece with the thread including controllinga vector direction of relative workpiece and thread movement;determining independently of controlling the movement the vectordirection of relative movement; and controlling a tension of the threadin response to the determined direction of relative movement to form anormally appearing stitch.

2. A method as in claim 1 wherein the formed stitch has a stitchabnormality and additionally comprising the step of drawing the stitchabnormality into the workpiece.

3. A method as in claim 1 wherein the step of determining the vectordirection of relative movement additionally comprises the step ofdetermining when a stitch abnormality is formed.

4. In a sewing machine having thread, stitch forming instrumentalitiesincluding a device for variably tensioning the thread, and means forcontrolling movement of a workpiece relative to the stitch forminginstrumentalities in vector directions, apparatus for forming a normallyappearing stitch comprising: means independent of the control ofmovement means for determining the vector direction of relative movementmeans responsive to the determined vector direction of workpiecemovement for controlling the variable thread tensioning device to form anormally appearing stitch.

5. A machine as in claim 4 wherein the stitch forming instrumentalitiesform a stitch abnormality and wherein the tension controlling meanscomprise means for drawing the abnormality into the workpiece.

6. A machine as in claim 4 additionally comprising means for determiningwhen a stitch abnormality is formed.

1. A method of forming a normally appearing stitch with a thread in arelatively movable workpiece and thread, comprising the steps of:forming a stitch in the workpiece with the thread including controllinga vector direction of relative workpiece and thread movement;determining independently of controlling the movement the vectordirection of relative movement; and controlling a tension of the threadin response to the determined direction of relative movement to form anormally appearing stitch.
 2. A method as in claim 1 wherein the formedstitch has a stitch abnormality and additionally comprising the step ofdrawing the stitch abnormality into the workpiece.
 3. A method as inclaim 1 wherein the step of determining the vector direction of relativemovement additionally comprises the step of determining when a stitchabnormality is formed.
 4. In a sewing machine having thread, stitchforming instrumentalities including a device for variably tensioning thethread, and means for controlling movement of a workpiece relative tothe stitch forming instrumentalities in vector directions, apparatus forforming a normally appearing stitch comprising: means independent of thecontrol of movement means for determining the vector direction ofrelative movement means responsive to the determined vector direction ofworkpiece movement for controlling the variable thread tensioning deviceto form a normally appearing stitch.
 5. A machine as in claim 4 whereinthe stitch forming instrumentalities form a stitch abnormality andwherein the tension controlling means comprise means for drawing theabnormality into the workpiece.
 6. A machine as in claim 4 additionallycomprising means for determining when a stitch abnormality is formed.